#3 What the numbers say

Football is a numbers game. How much one can actually rely on statistics in judging a player or different players is a matter of opinion. Some teams crunch numbers before they decide to buy a player. Other teams send scouts to see the player first hand and be judged instinctively by the football knowledge of the scout.
Van Dijk's stats this season are just marginally better than that of other top six defenders in the Premier League. He has played more games than all the other defenders and this contributes to the marginal difference.
Liverpool have kept the most clean-sheets of all the teams in the top six while Arsenal have kept the least. A comparison between Van Dijk and Mustafi does not show any such gap at all.
Van Dijk comes on top marginally in three categories: blocks, clearances and aerial battles won. Mustafi on the other hand, having played three games less than Van Dijk, has more interceptions, tackles, tackles won and headed clearances than Van Dijk.
When the Dutchman's stats are compared with that of players like Chiellini, Thiago Silva, Godin and Bonucci for this season, Van Dijk only comes on top in aerial duels won and total clearances made per game.
Different things are expected from defenders in different leagues and that contributes to an increase in numbers for defenders in a particular league on some defensive statistics. Van Dijk does not come out overwhelmingly on top after such considerations.
Van Dijk is capable of becoming the best defender in the world. His reading of the game, passing and aerial prowess are some of his biggest strengths and in time to come may elevate him to being the best defender in the world. However, he is by no means the best in the world right now.